Thus social life, in all its aspects and in every period of its history, is made possible only by a vast symbolism. The material emblems and figurative representations with which we are more especially concerned in our present study, are one form of this; but there are many others. Collective sentiments can just as well become incarnate in persons or formulæ: some formulæ are flags, while there are persons, either real or mythical, who are symbols. But there is one sort of emblem which should make an early appearance without reflection or calculation: this is tattooing. Indeed, well-known facts demonstrate that it is produced almost automatically in certain conditions. When men of an inferior culture are associated in a common life, they are frequently led, by an instinctive tendency, as it were, to paint or cut upon the body, images that bear witness to their common existence. According to a text of Procopius, the early Christians printed on their skin the name of Christ or the sign of the cross;[721] for a long time, the groups of pilgrims going to Palestine were also tattooed on the arm or wrist with designs representing the cross or the monogram of Christ.[722] This same usage is also reported among the pilgrims going to certain holy places in Italy.[723] A curious case of spontaneous tattooing is given by Lombroso: twenty young men in an Italian college, when on the point of separating, decorated themselves with tattoos recording, in various ways, the years they had spent together.[724] The same fact has frequently been observed among the soldiers in the same barracks, the sailors in the same boat, or the prisoners in the same jail.[725] It will be understood that especially where methods are still rudimentary, tattooing should be the most direct and expressive means by which the communion of minds can be affirmed. The best way of proving to one's self and to others that one is a member of a certain group is to place a distinctive mark on the body. The proof that this is the reason for the existence of the totemic image is the fact, which we have already mentioned, that it does not seek to reproduce the aspect of the thing it is supposed to represent. It is made up of lines and points to which a wholly conventional significance is attributed.[726] Its object is not to represent or bring to mind a determined object, but to bear witness to the fact that a certain number of individuals participate in the same moral life.